The Disadvantages of Using Thicker Oil in Your Engine – Jalopnik

The disadvantages of using thicker oil are inversely proportional to the effects of using thinner oil. One of the most notorious myths about motor oil is that thicker oil provides better protection than lower viscosity oil. However, this couldn’t be further from the truth as it all depends on the type of engine and the ambient temperature.

You will not immediately damage your engine if you decide to pour slightly thicker or thinner oil, but we always recommend that you stick to the prescribed oil viscosity in the owner’s manual. Why? Because the potential disadvantages outweigh the supposed advantages, and not all engines are built the same.

Suppose your car needs full synthetic oil 0W-20, but you insisted on pouring 10W-30 into it. As you probably know, the “W” stands for winter and the numbers refer to the viscosity of the oil, with a lower number meaning thinner oil. In this example, the fluid is a zero-weight oil when cold, and a 20-weight oil when the engine reaches its normal operating temperature, usually around 100 °C (212 °F).

In this case, the 0W-20 oil will flow faster than 10W-30 in winter, meaning it can lubricate faster on start-up and better protect against intense friction on cold starts. Switching to 10W-30, especially in winter, can do more harm than good, and the disadvantages include increased wear and tear and possible difficulty starting when the mercury drops.

The unwanted effects increase exponentially if you skip two degrees or more, for example if you go from the recommended 0W-20 to 15W-30. Modern engines typically require thinner oils due to tighter manufacturing tolerances in the main bearings and crankshaft journals. Thicker oil may not flow fast enough to protect these engines, and the pumping losses will ultimately lead to higher engine temperatures, premature sludge formation, and lower MPGs.

It may flow easier, but the oil can’t keep up with the lubrication if it gets too thin. This can result in devastating wear of bearings and internal components due to oil failure. Meanwhile, thinner oil also loses pressure, which can cause problems by affecting the engine’s variable valve timing, igniting the oil warning light, or causing valve noise. Depending on the climate, some car engines can run on different oils, such as 0W-20 or 5W-30. Choose 0W-20 if you ride in colder areas, but go for 5W-30 in warmer climates. This increases the level of protection when the engine needs it most.

Bottom line: Thicker oil isn’t necessarily better, but switching can be helpful if the owner’s manual says so. Otherwise, maintain the recommended oil viscosity at every oil change.